The application of metal nuclide nuclear magnetic resonance (NMR) as a probe for the structure of metal binding sites in biomolecules is being undertaken. Specifically, I=1/2 nuclei such as 205TI and 89Y are being studied. These nuclei can in many instances be substituted for K+ and Ca+2 in metal binding proteins. The nature of relaxation for I=1/2 nuclei allows the utility nuclear Overhauser enhancement (NOE) as a probe for measuring internuclear distances between the metal ion and selectively irradiated protons. The applicability of one- and two-dimensional NMR NOE experiments for such studies is being explored.